The present invention relates to a semiconductor device including a monitor light receiving element and a laser diode.
Such a semiconductor device is well known and commercially available as exemplified by ML4402 of Mitsubishi Denki Kabushiki Kaisha, HL7831G of Hitachi Ltd., and RLD-78A of Rome Inc., etc.
FIG. 1 is a partially cutaway perspective view of a basic structure of such a semiconductor device and FIGS. 2A and 2B are cross sections taken along lines A--A and B--B in FIG. 1, respectively. In these figures, a laser diode 1 is mounted through a sub-mount 3 on a block 2 bonded onto one surface of a stem 5. A light receiving element 4 is also bonded onto the same surface of the stem 5. Lead pins 6a, 6b and 6c extend from the other surface of the stem 5. The lead pin 6a is connected through a lead wire 7a to the laser diode 1 and the lead pin 6b is connected through a lead wire 7b to the light receiving element 4. A cap 8 having an opening 8a formed at a top thereof is fitted on a peripheral shoulder portion of the stem 5 to protect the laser diode/light receiving element assembly. The opening 8a is closed by a glass plate 9 through which an output laser beam is derived.
The laser diode 1 is disposed such that it can emit a laser beam vertically bidirectionally, an upward component of the laser beam being derived through the opening 8a of the cap 8 as the output laser beam. A downward component is used as a monitor laser beam. The latter is directed to the light receiving element 4 disposed on the stem 5 with a predetermined angle with respect to the latter. The output laser beam is controlled according to the monitor laser beam.
Since an operation of the laser diode 1 becomes unstable due to heat generated by the operation thereof, the block 2 is made of a high thermal conductivity material such as metal so that such heat is easily dissipated. Further, the sub-mount 3 disposed, between the laser diode 1 and the block 2 of, for example, silicon serves to eliminate a possible displacement of the laser diode 1 with respect to the block 2 due to a difference in thermal expansion therebetween.
The manufacture of such a semiconductor device includes a step of die-bonding the light receiving element 4 onto the stem 5 and then wire-bonding the lead wire 7b thereto, a step of bonding the laser diode 1 onto the block through the sub-mount 3 and then wire-bonding the lead wire 7a and a step of mounting the cap 8. That is, the die-bondings and wire-bondings are performed separately for the laser diode and the light receiving element.
Such separate bonding steps for the laser diode and the light receiving element causes the productivity of the semiconductor device to be low and the cost therefor to be high.